This invention relates to a thin film magnetic head having a coil which has a large cross-sectional area and high winding density, and more particularly to a thin film magnetic head having high reliability.
One example of the conventional thin film magnetic heads, such as the one that is disclosed in Japanese Patent Laid-Open No. 84020/1980, comprises upper and lower poles (magnetic cores) consisting of an Ni-19 wt. % Fe alloy (or the so-called "permalloy"), an insulating layer(s) separating both poles from each other, a signal input/output coil, and the like that are disposed on a nonmagnetic substrate.
Since recording density has been increased recently in magnetic recording/reproduction apparatuses such as disk drive systems, the development of a thin film magnetic head having high output and low noise has become essential. To develop such a thin film magnetic head, it is necessary to reduce the core length, to attain higher winding density of the coil and to increase the cross-sectional area of a coil conductor so as to reduce the electric resistance of the coil. However, all these are contradictory to one another from the aspect of coil production. Because the number of windings will drop if the core length is decreased or the cross-sectional area of the coil conductor will become small. The following two methods may be used to solve this problem.
One method is to laminate the coil as described in "Fabrication of Multitrack Thin Film Head" by Y. Noro et al., Journal of Applied Physics 53(3), March, 1982. However, this method involves a problem that the process is likely to be complicated. The other method is to reduce the pattern width of the coil conductor and its gap but increase the height of the coil conductor as described in "Lead Fabrication of Thin Film Magnetic Head for PCM Recording and Its Recording Performance", by Yamazaki et al., Digests of the 7th Annual Conference on Magnetics in Japan, Nov., 1983. Since this method finely patterns a thick film, etching residue is likely to occur, and hence selection of a mask material and selection of etching conditions must be optimized. The etching residue is formed in a projecting form at the upper edge portion of the coil conductor. In this case, discharge occurs between this projecting portion and the upper pole during the operation of the magnetic head and dielectric breakdown of the insulating layer is likely to occur.
During recording, the thin film magnetic head is used at a current density of about 10.sup.6 A/cm.sup.2, and by far severer requirement is imposed on the magnetic head in the aspect of electromigration resistance than the semiconductor device which is used generally at a current density of 10.sup.4 to 10.sup.5 A/cm.sup.2. Therefore, unlike the semiconductor device, it is necessary to use copper or copper alloy having extremely high electromigration resistance for the thin film magnetic head and to enlarge its cross-sectional area.